Modeling the Soret Effect in Dense Media Mixtures

A basic aim of this paper is to provide, as much as possible, a comprehensive and unambiguous description of the Soret effect in dense media. To this end, the available literature was examined for unifying themes; the themes found are presented. Many trends in the behavior of thermal diffusion coefficients are found to be correlated to equation-of-state properties. The evolutionary paths of media undergoing heating have the essential constraint of positive entropy production, as expressed by the theoretical relations of nonequilibrium thermodynamics; these are summarized. Also given are the relations between thermodynamic forces that define the path attractor states of media mixtures under steady heating conditions. Data references are given; almost all the available data relates to these asymptotic steady attractor states. There is little or no data available corresponding to the transient paths that are explicitly more dependent on the species diffusive transport mechanisms (rates). The concept of “heats of transfer” to express the thermal diffusion factors is verified to be generally valid for a slight modification of the defining relation as commonly presented. The heats of transfer are equivalent to an extension of kinetic theory thermal diffusion ratios. A discussion on the perspectives needed to properly form generic thermal diffusion models that are valid for any particular situation is given.